Australia's bearded dragons have a weird sex-changing behavior that could ultimately drive the population to extinction

The Australian bearded
dragon can change its sex based on the
temperature.Arthur
Georges

Sex in the reptile world is
full of surprises — like lizards that change sex in response to
the climate.

That's right: In warm environments, a type of lizard known as the
Australian bearded dragon can switch from having its sex
determined by genes to having it determined by temperature.

Some types of fish can reverse
their sex — for example, parrotfish start life as females and
change to males. In rare cases, some
amphibians like the
common reed frog and crested newt larvae can
too. But this case, described in
astudypublished
Wednesday, July 1, is the very first time scientists have
documented wild reptiles changing their sex in
response to the temperature.

It was a shocking discovery,
even to the researchers:

"We thought we knew it all about sex," study researcher and
University of Canberra in Australia ecologist Arthur Georges told
Business Insider. "But along came our little dragon."

Arthur Georges

Typically, bearded dragons inherit two
sex chromosomes — one from each of their parents —
just like humans. (Instead of an X and a Y chromosome, they get a
Z and a W chromosome; boy lizards are ZZ and girl lizards are
ZW.)

For their study, Georges and his colleagues captured 131 wild
adult bearded dragons from different parts of Australia and
brought them back to their lab in Canberra to breed them. The
researchers could tell what sex the lizards
were based on the
presence or absence of male sex organs called
hemipenes.

After the females laid eggs, the researchers
moved them to a separate container to incubate them until they
hatched. Theysequenced the lizards' sex chromosomes to
determine their genetic sex. Curiously, 11 of the lizards (the ones from
the warmest areas
they sampled) had a male set of chromosomes
(ZZ), but in all other
ways were female.Arthur Georges

Even more surprisingly, the offspring of the
sex-changing lizards had a sex that
was determined by temperature alone. Within one
generation, the W chromosome was completely eliminated
from that population. And "once that chromosome is
gone, it's really hard to flip back, because once you've thrown
that machinery away, to reinvent it takes a long time," Georges
said.

The sex-reversed females also tended to lay about twice as
many eggs as normal girl lizards, so over time, this resulted in
a largely female population.

Scientists aren't sure why the lizards evolved this ability to
change sex, but one possibility is that is gives them more
flexibility to live in different environments. But it could also
mean the lizards may be more susceptible to the effects
of climate change, because their population could end up
becoming 100% female.

"If the climate kept on warming four to five degrees, it could be
quite catastrophic, and could drive the lizards to extinction,"
Georges said.